List of top Mechanical Engineering Questions on Thermodynamics asked in AP PGECET

A heat engine operates between a hot source at \(T_{\text{H}} = 900\text{ K}\) and a cold sink at the ambient temperature \(T_{0} = T_{\text{C}} = 300\text{ K}\). During one cycle the engine receives \(Q_{\text{H}} = 12,000\text{ kJ}\) from the hot source and rejects \(Q_{\text{C}} = 8,000\text{ kJ}\) to the cold sink. Which of the following statements is correct?

The shape factor in radiative heat transfer depends on:

In a reversed Brayton refrigeration cycle, the refrigerating effect is increased if

During an adiabatic process in an ideal gas, which of the following is true?

A closed system undergoes a process in which it interacts with the surroundings maintained at \(T_{0} = 300\text{ K}\) and \(P_{0} = 100\text{ kPa}\). During the process:
\(\bullet\) The system receives 1000 kJ of heat from a reservoir at 1200 K.
\(\bullet\) The system does 500 kJ of boundary work on the surroundings.
\(\bullet\) There is no change in kinetic or potential energy, and the process ends at the dead state (equilibrium with surroundings).
Which of the following statements is most correct?

For an air-standard Otto cycle, the compression ratio is 8 and the ratio of specific heats (\(\gamma\)) is 1.4. The air-standard efficiency of the cycle is _______.

In a counter flow heat exchanger, hot fluid enters at \(120^\circ\text{C}\) and leaves at \(80^\circ\text{C}\). Cold fluid enters at \(20^\circ\text{C}\) and leaves at \(60^\circ\text{C}\). Find the log mean temperature difference (LMTD).

Air enters an adiabatic nozzle at 300 kPa and 500 K with a velocity of 10 m/s. It leaves the nozzle at 100 kPa with a velocity of 180 m/s. The specific heat of air \(C_{\text{p}} = 1008\text{ J/kg}\cdot\text{K}\). The exit temperature of air is

Consider a simple gas turbine (Brayton) cycle and a gas turbine with perfect regeneration. In both the cycles, the pressure ratio is 6 and the ratio of the specific heats of the working medium is 1.4. The ratio of minimum to maximum temperatures is 0.3 (with temperatures expressed in K) in the regenerative cycle. The ratio of the thermal efficiency of the simple cycle to that of the regenerative cycle is

Which of the following processes is isobaric?

Heat transfer of 800 kJ occurs from a source at 500 K to surroundings at 300 K. Calculate maximum available work.

If a heat exchanger has effectiveness = 1, it means:

Water (\(C_{\text{p}} = 4.18\text{ kJ/kg}\cdot\text{K}\)) at \(80^\circ\text{C}\) enters a counter-flow heat exchanger with a mass flow rate of \(0.5\text{ kg/s}\). Air (\(C_{\text{p}} = 1\text{ kJ/kg}\cdot\text{K}\)) enters at \(30^\circ\text{C}\) with a mass flow rate of \(2.09\text{ kg/s}\). If the effectiveness of the heat exchanger is 0.8, the LMTD (\(^\circ\text{C}\)) is

The Number of Transfer Units (NTU) method is primarily used to:

What is the significance of availability (or exergy) in thermodynamics?

The emissivity of a grey surface is:

For a closed, simple compressible system, which of the following thermodynamic relations is always valid, irrespective of the process, assuming only reversible processes and equilibrium states?

The logarithmic mean temperature difference (LMTD) method is used to:

A solid sphere has characteristic length $L_c = 0.02\text{ m}$, thermal conductivity $K = 40\text{ W/mK}$, and convective heat transfer coefficient $h = 10\text{ W/m}^2\text{K}$. Find the correct statement.

A surface behaves as a perfect black body at 600 K. Another black body is at 300 K. The ratio of emissive powers is:

A cylinder contains $5\text{ m}^3$ of an ideal gas at a pressure of 1 bar. The gas is compressed in a reversible isothermal process until the pressure increases to 5 bar. Determine the work required for this compression (kJ).

Air (ideal gas) enters a perfect insulated compressor of a temperature of 310 K. The pressure ratio of compressor is 6, Specific heat at constant pressure for air 1005 J/kgK and ratio of specific heats at constant pressure and constant volume is 1.4. Assume that specific heat of air is constant. If the isentropic efficiency of the compressor is 85 percent, the difference in enthalpies of air between the exit and inlet of the compressor is _______

In a Carnot cycle, which process occurs between the two isothermal processes?

One kg of air, initially at a temperature of $127\text{ }^{\circ}\text{C}$ expands reversibly at a constant pressure until the volume is doubled. If the gas constant of air is $287\text{ J/kg K}$, the magnitude of work transfer is _______ kJ.

The compressor of a gas turbine plant, operating on an ideal intercooled Brayton cycle, accomplishes an overall pressure ratio of 6 in a two-stage compression process. Intercooling is used to cool the air coming out from the first stage to the inlet temperature of the first stage, before its entry to the second stage. Air enters the compressor at 300 K and 100 kPa. If the properties of gas are constant, the intercooling pressure for minimum compressor work is _______